Periodic Micro/Nano-Ripples Structures On Silicon And Germanium Surface By Femtosecond Laser

Biological surfaces with periodic structures in nature have some unique function structures and survival mode, such as structural color, superhydrophobic, anti-reflective and super adhesion. Because the biological surfaces with specific structures provide human with inspiration, the surface periodic ripples structures have been studied extensively. Laser-induced periodic surface structures (LIPSSs) are applied in the fields of photonics, microelectronics, optoelectronics, nanofluidics and biomedicine. Silicon and germanium are important semiconductor materials, and surfaces with LIPSSs have a lot of potential applications, including solar cells, flat panel displays and enhanced surface plasmon. With the advent of femtosecond laser, novel surface structures such as the high spatial frequecy LIPSSs (HSFLs) have been made, and the formation mechanism of HSFLs is still controversially discussed. In this paper, we studied the preparation conditions and formation mechanisms of the periodic ripples structures on silicon and germanium under femtosecond laser irradiation.LSFLs, HSFLs and periodic grooves structures are formed by femtosecond laser irradiation at repetition rate of 76 MHz and 1 kHz on monocrystalline silicon. The effects of laser pulse energy, number of laser pulse, laser polarization and environments on silicon surface morphology are studied, and a revised Sipe-Drude interference theory is developed. HSFLs with orientation parallel to the laser polarization are firstly made by using high repetition rate femtosecond laser pulses. The revised Sipe-Drude interference theoretical results show good agreement with the periods and orientations of LSFLs and HSFLs, and we consider the surface plasmon polaritons (SPPs) excited upon irradiation of solid materials with femtosecond laser play important roles in LSFLs and HSFLs.Meanwhile, the sub-100 nm HSFLs and LSFLs are generated by femtosecond laser irradiation at repetition rate of 76 MHz and 1 kHz on monocrystalline germanium. The ripples periods of the germanium surface are mainly related to the laser pulse energy, the number of laser pulses per irradiation spot and laser wavelength. The interference between the spatial harmonics of SPPs is the major reason in LSFLs and HSFLs with orientation perpendicular or parallel to the laser polarization.With the preparation of the periodic ripples structures on the monocrystalline silicon and germanium surface by femtosecond pulse laser irradiation, the formation mechanism of HSFLs was in-depth explored. We have developed a new route for femtosecond laser fabrication nano-materials.